1. Field of the Invention
The present invention relates to a self-supporting inflatable dual wall structure and more specifically of a type utilized for forming roof structures and other lightweight, large span, self-supporting, open structures.
2. Description of the Prior Art
Numerous attempts have been made to provide a pneumatic dual wall roof or cover made of lightweight fabric or synthetic material. One type includes a cellular construction as shown in U.S. Pat. Nos. 3,247,627, Bird, 1966; 3,030,640, Gosman, 1962; 3,779,847, Turner, 1973; 511,472, Sumovski, 1893; 2,837,101, Bary, 1958; 3,256,649, Webb, 1966; 3,292,338, MacClarence et al, 1966; 4,186,530, Fraioli, 1980; 3,973,363, LaPorte et al, 1976 and 3,227,169, Fischer, 1966.
Another form of dual wall inflatable structure is the type shown in U.S. Pat. No. 4,004,380, Kwake, 1977, in which two membranes form the inflatable structure and tension rods or tension cables extend between anchor points on the membranes. Examples of this type of structure are shown in U.S. Pat. Nos. 3,123,085, Demarteau, 1964; 2,753,019, Phane, 1956; 2,743,510, Mauney et al, 1956; 2,698,020, Phane, 1954; 2,657,716, Ford, 1953; 2,636,457, Finlay et al, 1953; 2,016,054, Sentell, 1935; and 3,277,614, Marie, 1966.
The Marie patent, for instance, shows a framework of cables forming a beam or girder surrounded by a cover, the cover including prisoner cables attached to nodes formed from connecting cables resulting from the triangular structure of the framework. The resulting structure shown in FIGS. 7 and 8, is a complex unidirectional inflated girder or beam.